隨著近年來發光二極體效率逐步提升，發光二極體用為照明光源的可能性也越來越高。欲開拓這個新的領域，除了發光效率、發光強度需達一般照明的需求外，如何運用發光二極體本身去突顯其照明的獨特性，才是真正的利基市場。
結合多顆不同顏色發光二極體的多晶粒發光二極體(Multi-chip LED)為一可行的方式。此類的發光二極體，除可避免因為螢光粉轉換的能量損失，得到較佳的發光效率外，更藉由分開控制各顆發光二極體的光色及強度，達到全彩的變色效果(可變色溫)。但由於各色發光二極體特性的不同，而造成光源輸出偏移目標色的情形，為了解決這類的問題，過去是利用光學回饋的方式去修正其輸出結果。此類系統仰賴的光感測器，不但限制了設計上的自由度，也額外增加了整體的成本。
本論文提出一個方法用來預測在不同操作情況下，多晶粒發光二極體的光譜分佈。本方法藉由建立一個成功模型，掌握二個重要的基本特性: 一為建立一個以驅動電流及接面溫度為參數的光譜模型；二為使用熱阻矩陣的方式去估算周遭晶粒的熱影響及各顆晶粒最後的接面溫度，達成預測光譜分佈的目標。經由實驗的驗證，實際光譜與模擬結果的色差可以被控制在0.01以內，符合照明規範之標準。本論文說明如何結合上述方法，達成預測光譜分佈的目標。藉由這樣的方式，可避開光感測器的使用，降低此類產品的成本。

The rapid development of high efficacy and high-brightness light emitting diodes (LED) in recent years has made LEDs a very promising light source in the future. Among general approaches using LED to achieve white light, the multi-chip LED module approach provides a unique feature of color variability, i.e. control the color characteristics of a light source by changing the drive current.
In a multi-chip LED module, each chip has a different spectral property, to control the module dynamically, it is necessary to incorporate a color sensor into the module. However, it adds the complexity to the driving and control circuits, as well as the cost and reduces design flexibility.
In this work, we propose a method for predicting the performance of a multi-chip LED module under various operating conditions. The method essentially includes two parts: firstly, it employs an emission spectrum model which depends upon driving current and junction temperature, and, secondly, it applies a compact model to determine the junction temperature of each individual chip. Using this method, we have demonstrated the feasibility of determining the spectrum distribution of the multi-chip LED module using red, green, blue and amber colors.
We have further demonstrated experimentally in this work, the color difference between the measured spectra and the modeling result can be controlled within 0.01 or less. This result satisfied the recommended deviation limit dictated by the lighting industry. Therefore, the performance of multi-chip LED module can be controlled accurately by an external feedback system without requiring a costly color sensor. This way, it could reduce the cost of a multi-chip LED module used for general lighting application.

[1] 蘇炎坤, 林俊良, “白光發光二極體之發展”, EDMA電子資訊九卷二期-光電技術專刊, p.54-66, (2003)

[2] E. Fred Schubert and Jong Kyu Kim, “Solid-State Light Sources Getting Smart”, SCIENCE, Vol. 308, p.1274-1278, (2005)

[3] E. Fred Schubert, “Light-Emitting Diodes”, 2nd edition, Chapter 16-19 (2006)

[4] S. Chhajed, Y. Xi, Th. Gessmann, J.-Q. Xi, J. M. Shah, J. K. Kim and E. F. Schubert, “Junction temperature in light-emitting diodes assessed by different methods”, Proc. of SPIE, Vol. 5739, p.16-24, (2005)

[5] Lalith Jayasinghe, Yimin Gu and Nadarajah Narendran, “Characterization of thermal resistance coefficient of high-power LEDs”, Proc. of SPIE, Vol.6337, (2006)

[6] Y. Xi and E. F. Schubert, “Junction-temperature measurement in GaN ultraviolet light-emitting diodes using diode forward voltage method, APPLIED PHYSICS LETTERS, Vol. 85, p.2163-2165, (2004)

[7] “Thermal Design Considerations for Luxeon 5 Watt Power Light Sources”, Lumileds Technical Datasheet AB23 (2003)

[8] G. Farkas, Q. van Voorst Vader, A. Poppe and G. Bognár, Proc. of 9th THERMNIC Workshop, Sept. 24-26, p.213-218, (2003)

[9] http://www.kruschwitz.com/cri.htm

[10] Angel García-Botella, Antonio Alvarez Fernández-Balbuena, Daniel Vázquez-Moliní and Eusebio Bernabeu, “Thermal influences on optical properties of light-emitting diodes: a semiempirical model”, APPLIED OPTICS, Vol. 40,
No. 4, (2001)

[11] Y.-L. Li, J. M. Shah, P. H. Leung, Th. Gessmann and E. F. Schubert, “Performance characteristics of white light sources consisting of multiple light-emitting diodes”, Proc. of SPIE, Vol. 5187, p.178-184, (2004)

[12] Yoshi Ohno, “Color Rendering and Luminous Efficacy of White LED Spectra”, Proc. of SPIE, Vol. 5530, p.88-98, (2004)

[13] Kwong Man and Ian Ashdown, “Accurate Colorimetric Feedback for RGB LED Clusters”, Proc. of SPIE, Vol.6337, (2006)

[14] Hung-Yu Chou, Tsung-Hsun Yang, “Novel Formula for Emission Spectrum of Light Emitting Diodes”, Proceedings of OPT 2005, A-SA-I11-1, (2005)

[15] Hung-Yu Chou, Tsung-Hsun Yang, “Dependence of Junction Temperature and Driving Current upon Emission Spectra of Light Emitting Diodes”, Proceedings of OPT 2006, (2006)

[16] Theo Treurniet and Vicky Lammens, “Thermal Management in Color Variable Multi-Chip LED Modules”, 22nd IEEE SEMI-THERM Symposium, (2006)

[17] Lan Kim, Jonghwa Choi, Sunho Jang and Moo Whan Shin, “Thermal Analysis of Multi-chip LED Packages”, Proc. of SPIE, Vol.6355, (2006)

[18] MathWorks, MATLAB 7.0, (2004)